Carbon fiber-carbon matrix composites (sometimes referred to as "carbon-carbon composites") and ceramic fibers coated with carbon in a carbon matrix are a class of materials whose properties are especially suitable for use at elevated temperatures. The temperature capability of carbon-based composites makes them exceptionally attractive for various aerospace applications, including gas turbine engines. The most significant drawback in the use of carbon-based composites in high temperature applications is the susceptibility of carbon-based materials to oxidize at high temperatures.
Carbon fibers are particularly attractive for use in various applications, since the carbon fibers can be formed into a cloth and the cloth can be preformed into various desired shapes prior to final formation of a desired part. Carbon fiber materials are usually produced starting with an organic precursor fiber, such as polyacrylonitrile, rayon or pitch. Such fibers are usually produced in the form of yarn, often by an extrusion process. The precursor fibers are heated in an inert atmosphere to pyrolyze or carbonize the fibers and may then be heated to a higher temperature to form graphite fibers. These carbon graphite materials may then be laid down, woven or interleaved to form various structures depending on the number and weave of the fibers. The woven structures can then be impregnated with a pitch or resin matrix material which is converted to carbon and then graphite to form a carbon-carbon fiber composite. In this process, hot pressing is also employed to obtain a dense structure. Repeated impregnation steps can be employed to increase density. Carbon fiber-carbon matrix composites can also be formed by chemical vapor infiltration to deposit a pyrolytic graphite matrix.
It is well known in the prior art to use silicon carbide conversion coatings employing a pack coating process to protect carbon-based materials, including carbon-based composites. The coatings are referred to as conversion coatings because the surface of the article to be coated, i.e., a carbon-based composite, is converted to silicon carbide by reacting it with silicon. Pack coating refers to processes wherein a carbon-based material is embedded and heated in a pack material which produces silicon or silicon compound vapors when heated. Pack compositions based on aluminum oxide, silicon and silicon oxide are known.
U.S. Pat. No. 4,544,412 to Veltri, et al. is directed to a particular pack material for the formation of silicon carbide coatings on carbon-carbon composite materials. A pack coating refers to the method for providing the silicon carbide coating wherein a carbon-carbon composite is dispersed in a powdered pack and is heated while in contact with the pack material. The pack material of the Veltri et al. patent consists of about 60% silicon carbide powder, about 30% silicon powder, about 1% boron powder and about 9% aluminum oxide powder.
U.S. Pat. No. 4,267,211 to Yajima, et al. describes a process for producing a shaped article having resistance to corrosion, heat and oxidation. In the method, a shaped article is coated with a coating composition comprising a organometallic compound and the coated article is subjected to heat treatment. The shaped article is composed of at least one material selected from metals, carbonaceous substances, and ceramics. The organometallic compound comprises at least one polymer selected from the group consisting of polycarbosilanes and polycarbosiloxanes. U.S. Pat. No. 4,915,760 to Singh, e al. teaches depositing an organic slurry of ceramic particles onto parallel boron-coated filaments of silicon carbide and hot pressing a multilayered stack.
Additions of boron compounds and boron throughout a matrix of carbon-base materials to reduce oxidation sensibility is also known as set forth in U.S. Pat. No. 3,672,936 to Ehrenreich. The Ehrenreich patent discloses a reinforced carbon article which comprises a carbon fiber shape bonded by a carbon binder and having incorporated within the carbon shape, the in situ reaction product of carbon and a boron containing additive. The boron containing additive is a material selected from the group consisting of boron, boron nitride, boron silicide and refractory metal borides. The method of the Ehrenrich patent comprises forming a carbon fiber shape, dispersing the boron containing additive within at least a portion of the carbon fiber shape, impregnating the carbon fiber shape with a carbonizable binder and heating the carbon fiber shape to carbonize the binder and to form in situ the reaction product of carbon and the boron containing additive.
U.S. Pat. No. 4,892,790 to Gray discloses making oxygen-resistant composites with carbon fibers dispersed within a carbonaceous matrix formed from a phenolic resin mixture which contains boron and silicon.
U.S. Pat. No. 4,923,719 teaches coating of silicon carbide fibers with an organosilane for use in fiber reinforced composites.
While various processes are known for making carbon-carbon composites, it would be desirable to provide a simple and inexpensive method for making composites wherein carbon fibers are embedded in a matrix of silicon carbide.
Accordingly, it is a principal object of the present invention to provide a method for producing a silicon carbide composite utilizing carbon-based fiber cloth materials.